The present invention relates to novel compounds that are inhibitors of the receptor tyrosine kinases AXL and c-MET. The compounds are suitable for treatment of AXL or c-MET-mediated disorders such as cancer, and the development of resistance to cancer therapies.
Receptor tyrosine kinases (RTKs) are transmembrane proteins that transduce signals from the extracellular environment to the cytoplasm and nucleus to regulate normal cellular processes, including survival, growth, differentiation, adhesion, and mobility. Abnormal expression or activation of RTKs has been implicated in the pathogenesis of various human cancers, linked with cell transformation, tumor formation and metastasis. These observations have led to intense interest in the development of tyrosine kinase inhibitors as cancer therapeutics (Rosti et al, Crit. Rev. Oncol. Hematol. 2011. [Epub ahead of print]; Gorden et al, J. Oncol. Pharm. Pract. 2011. [Epub ahead of print]; Grande et al, Mol. Cancer Ther. 2011, 10, 569).
AXL is a member of the TAM (TYRO3, AXL, MER) receptor tyrosine kinase (RTK) family originally identified as a transforming gene expressed in cells from patients with chronic myelogenous leukemia (O'Bryan et. al Mol. Cell Biol. 1991, 11, 5016) or chronic myeloproliferative disorder (Janssen et. al Oncogene, 1991, 6, 2113). AXL activation occurs by binding of its cognate protein ligand, growth arrest specific 6 (Gas6), homotypic dimerization through its extracellular domain or cross-talk via the interleukin (IL)-15 receptor or HER2. AXL signaling stimulates cellular responses, including activation of phosphoinositide 3-kinase-Akt, extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase cascades, the NF-κB pathway, and signal transducer and activator of transcription (STAT) signaling (Hafizi et. al Cytokine Growth Factor Rev., 2006, 17, 295). Numerous biological consequences of AXL signaling, including invasion, migration, survival signaling, angiogenesis, resistance to chemotherapeutic and targeted drugs, cell transformation, and proliferation, represent undesirable traits associated with cancer (Linger et al. Adv. Cancer Res., 2008, 100, 35; Hafizi et. al Cytokine Growth Factor Rev., 2006, 17, 295; Holland et al, Cancer Res. 2005, 65, 9294).
AXL receptors regulate vascular smooth muscle homeostasis (Korshunov et al, Circ. Res. 2006, 98, 1446) and are implicated in the control of oligodendrocyte cell survival (Shankar et al, J. Neurosci. 2003, 23, 4208). Studies in knockout mice have revealed that TAM receptors play pivotal roles in innate immunity by inhibiting inflammation in macrophages and dendritic cells (Sharif et al, J. Exp. Med. 2006, 203, 1891; Rothlin et al, Cell. 2007, 131, 1124), promoting the phagocytosis of apoptotic cells (Lu et al, Nature. 1999, 398, 723; Lu & Lemke, Science. 2001, 293, 306; Prasad et al, Mol. Cell Neurosci. 2006, 3, 96) and stimulating the differentiation of natural killer cells (Park et al, Blood 2009, 113, 2470).
AXL has been found to be constitutively activated due to gene amplification and/or altered protein expression (O'Bryan et al, J. Biol. Chem. 1995, 270, 551; Linger et al, Expert Opin. Ther. Targets. 2010, 14, 1073; Mudduluru et al, Oncogene, 2011, 30, 2888). Altered expression of AXL has been reported in a variety of human cancers (Crosier et al, Leuk. Lymphoma. 1995, 18, 443; Challier et al, Leukemia, 1996, 10, 781; Ito et al, Thyroid. 1999, 9, 563; Sun et al, Oncology. 2004, 66, 450; Green et al, Br. J. Cancer. 2006, 94, 1446; Liu et al, Blood. 2010, 116, 297) and is associated with invasiveness and metastasis in lung cancer (Shieh et al, Neoplasia. 2005, 7, 1058), prostate cancer (Shiozawa et al, Neoplasia. 2010, 12, 116), breast cancer (Zhang et al, Cancer Res. 2008, 68, 1905), esophageal cancer (Hector et al, Cancer Biol. Ther. 2010, 10, 1009), ovarian cancer (Rankin et al, Cancer Res. 2010, 70, 7570), pancreatic cancer (Koorstra et al, Cancer Biol. Ther. 2009, 8, 618; Song et al, Cancer, 2011, 117, 734), liver cancer (He et al, Mol. Carcinog. 2010, 49, 882), gastric cancer (Wu et al, Anticancer Res. 2002, 22, 1071; Sawabu et al, Mol Carcinog. 2007, 46, 155), thyroid cancer (Avilla et al, Cancer Res. 2011, 71, 1792), renal cell carcinoma (Chung et al, DNA Cell Biol. 2003, 22, 533; Gustafsson et al, Clin. Cancer Res. 2009, 15, 4742) and glioblastoma (Hutterer et al, Clin. Cancer Res. 2008, 14, 130).
Indeed, AXL overexpression is associated with late stage and poor overall survival in many of those human cancers (Rochlitz et al, Leukemia, 1999, 13, 1352; Vajkoczy et al, Proc Natl. Acad. Sci. 2006, 103, 5799). AXL contributes to at least three of the six fundamental mechanisms of malignancy in human, by promoting cancer cell migration and invasion, involving in tumor angiogenesis, and facilitating cancer cell survival and tumor growth (Holland et al, Cancer Res. 2005, 65, 9294; Tai et al, Oncogene. 2008, 27, 4044; Li et al, Oncogene, 2009, 28, 3442; Mudduluru et al, Mol. Cancer Res. 2010, 8, 159). AXL is strongly induced by epithelial-to-mesenchymal transitions (EMT) in immortalized mammary epithelial cells and AXL knockdown completely prevented the spread of highly metastatic breast carcinoma cells from the mammary gland to lymph nodes and several major organs and increases overall survival (Gjerdrum et al, Proc. Natl. Acad. Sci. USA. 2010, 107, 1124; Vuoriluoto et al, Oncogene. 2011, 30, 1436), indicating AXL represents a critical downstream effector of tumor cell EMT requiring for cancer metastasis.
AXL is also induced during progression of resistance to therapies including imatinib in gastrointestinal stromal tumors (Mahadevan et al, Oncogene. 2007, 26, 3909) and Herceptin and EGFR inhibitor therapy (e.g. lapatinib) in breast cancer (Liu et al, Cancer Res. 2009, 69, 6871) via a “tyrosine kinase switch”, and after chemotherapy in acute myeloid leukemia (Hong et al, Cancer Lett. 2008, 268, 314). AXL knockdown was also reported to lead to a significant increase in chemosensitivity of astrocytoma cells in response to chemotherapy treatment (Keating et al, Mol. Cancer Ther. 2010, 9, 1298). These data indicate AXL as an important mediator for tumor resistance to conventional chemotherapy and molecular-based cancer therapeutics.
The c-MET receptor was initially identified as the TPR-MET oncogene in an osteosarcoma cell line treated with a chemical carcinogen. The TPR-Met protein is able to transform and confer invasive and metastatic properties to non-tumorigenic cells (Sattler et. al, Current Oncology Rep., 2007, 9, 102). The oncogenic potential is a result of spontaneous dimerization and constitutive activation of TPR-MET. Aberrant expression of HGF and c-MET is associated with the development and poor prognosis of a wide range of solid tumors, including breast, prostate, thyroid, lung, stomach, colorectal, pancreatic, kidney, ovarian, and uterine carcinoma, malignant glioma, uveal melanoma, and osteo- and soft-tissue sarcoma (Jaing et. al Critical Rev. Oncol/Hematol., 2005, 53, 35). Gastric tumors with an amplification of the wt-c-MET gene are more susceptible to MET inhibition, thereby making c-MET an attractive target (Smolen et. al Proc. Natl. Acad. Sci. USA, 2006, 103, 2316).
In vitro and in vivo studies have shown that increased and dysregulated c-MET activation leads to a wide range of biological responses associated with the malignant phenotype. These responses include increased motility/invasion, increased tumorigenicity, enhanced angiogenesis, protection of carcinoma cells from apoptosis induced by DNA-damaging agents such as adriamycin, ultraviolet light, and ionizing radiation, and enhanced rate of repair of DNA strand breaks [Comoglio et. al J. Clin. Invest., 2002, 109, 857, Sattler et. al Current Oncology Rep., 2007, 9, 102; Fan et. al, Mol. Cell Biol., 2001, 21, 4968). Based upon these data, HGF may enhance mutagenicity following DNA damage, allowing tumor cells with genetic damage to survive, and thus leading to resistance to chemo- and radiotherapeutic treatment regimens (Fan et. al, Mol. Cell Biol., 2001, 21, 4968; Hiscox et. al Endocrine-Related Cancer, 2004, 13, 1085).
MET amplification plays a unique critical role in mediating resistance of non-small cell lung cancer to EGFR inhibitors (e.g. Tarceva™, Iressa™, Tykerb™) the resistance of HER2 positive breast cancer to trastuzumab (Sattler et. al, Update Cancer Ther., 2009, 3, 109; Engleman et. al, Science, 2007, 316, 1039, Shattuck et. al Cancer Res., 2008, 68, 1471, Agarwal et. al, Br. J. Cancer, 2009, 100, 941; Kubo et. al, Int. J. Cancer 2009, 124, 1778). Inhibition of c-MET in Tarceva™ or Iressa™ resistant cells using shRNA or small molecules alone or in combination with an EGFR inhibitor overcame MET-mediated resistance to EGFR inhibitors [Agarwal et. al, Br. J. Cancer, 2009, 100, 941; Bachleitner-Hoffman et. al, Mol. Cancer Ther., 2008, 7, 3499, Tang et. al, Br. J. Cancer, 2008, 99, 911; Bean et. al, Proc. Natl. Acad. Sci. USA, 2007, 104, 20932). Due to the pleiotropic, pro-tumorigenic activities of the HGF-c-MET axis, inhibiting this pathway would be predicted to have potent anti-tumor effects in many common cancers through multiple complimentary mechanisms.
A need exists for AXL and c-MET inhibitors for use as pharmaceutical agents.